<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<body>


<script>

    const PI = '3.14'; // 只读变量
    console.log(PI);
    PI = '123'; // TypeError: Assignment to constant variable.
    console.log(PI);

</script>

</body>
</html>